There is a known capacitor life determining device which is connected to a DC-DC converter and a load circuit and determines whether or not an output capacitor of the DC-DC converter is at the end of life (refer to Patent Document 1). The DC-DC converter has the output capacitor than is charged by a direct-current power supply, a switching element that turns on/off the charge from the direct-current power supply to the output capacitor, and a control unit. The control unit periodically drives on/off of the switching element, detects a voltage between both ends of the output capacitor, and decides the on-duty of the switching element by feedback control of bringing the voltage between both ends of the output capacitor to a predetermined target voltage. The load circuit is a load circuit that converts output power of the DC-DC converter and outputs it to the load, and varies the output power to the load according to an input from the outside. The capacitor life determining device includes a load control unit, a voltage detecting unit, and a life determining unit. The load control unit periodically performs determination control of temporarily changing the output power of the load circuit, at an interval longer than the duration of the determination control. The voltage detecting unit detects at least an alternating-current component of the voltage between both ends of the output capacitor immediately after the determination control is started. The life determining unit determines whether or not the output capacitor is at the end of life, on the basis of the amplitude of the voltage between both ends detected by the voltage detecting unit.
There also is a known switching power supply device that generates a direct-current voltage by rectifying and smoothing an alternating-current input and generates an output voltage by switching, transforming, and rectifying and smoothing the direct-current voltage, and has an electrolytic capacitor for smoothing processing (refer to Patent Document 2). The switching power supply device has a process of measuring the frequency of the alternating-current input, a process of measuring the output voltage and the output current, and a process of measuring the voltage between both ends of the electrolytic capacitor. The switching power supply device further has a process of converting, on the basis of the measured frequency, output voltage and output current and a terminal voltage of the electrolytic capacitor, the terminal voltage into a terminal voltage at the time when applying a rated load. Further, the switching power supply device has a process of comparing the converted terminal voltage with a predetermined initial value of the terminal voltage to determine a decrease in electrostatic capacitance of the electrolytic capacitor.
Patent Document 1: Japanese Laid-open Patent Publication No. 2011-97683
Patent Document 2: Japanese Laid-open Patent Publication No. 2000-308339
Patent Document 1 is intended to determine whether or not the output capacitor is at the end of life at the present moment. Besides, Patent Document 2 is intended to determine the decrease in electrostatic capacitance of the electrolytic capacitor. However, Patent Documents 1 and 2 cannot report the residual life of the capacitor.